Complicated nature of the gap in MgB2: magnetic field-dependent optical studies

TL;DR

This study explores how magnetic fields affect the optical properties of MgB2 thin films, revealing complex behavior in the superconducting gap that challenges simple models.

Contribution

It provides detailed magnetic field-dependent optical conductivity measurements of MgB2, highlighting the complex nature of its superconducting gap.

Findings

Normal metallic regions increase with magnetic field

Area fraction of normal regions grows quickly at low fields

Superconducting gap behavior is more complicated than simple models

Abstract

We investigated the magnetic field (H)-dependent optical conductivity spectra of MgB2 thin film in the far-infrared region. The H-dependences can be explained by the increase of normal metallic regions embedded in the superconducting background. The area fraction of the normal metallic region increases rather quickly at low field, but slowly at high field. It follows neither H- nor H^{1/2}-dependences. The results suggest the complicated nature of the superconducting gap in MgB2.